How to Build a City on the Moon

Andy Weir is back with a new book. And while The Martian followed a wisecracking astronaut marooned on Mars, Artemis (out now) follows a wisecracking, ne'er-do-well young woman who lives in the titular city, which happens to be humanity's first permanent outpost on the moon.

As with Weir's breakout title, science is the star of the show. Artemis is at its strongest when Weir dives into deep explanations of how the city works and the technology required to build a lunar base. The book takes place many decades from now, but Weir tells PopMech that (nearly) all the tech required to build and sustain Artemis exists today. Here's how he did it. (Only very mild spoilers ahead.)

The Why and the How

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Before he laid out the fictional city of Artemis and worked out its mechanics, Weir started with a basic question: Why would anybody go to the trouble of building a town on the moon in the first place. To him it had only one workable answer: tourism.

Artemis is a tourist villa. It's inspired by the resort towns of the Caribbean, which are dominated by glimmering hotels for the moneyed travelers and "austere conditions for the residents," Weir says. (Our heroine, Jazz, lives in a closet with a bed stuffed in it.)

The city's very location is beholden to its main industry. If you could build a city anywhere on the moon, Weir says, you'd do it in aluminum-rich lunar highlands near the materials you'd need to construct the place (more on that later). But Artemis is located in lowland terrain because that's what you find near the historic Apollo 11 landing site where future moon tourists want to go.

As a result, the city of Artemis is a compromise. It lies near a lunar feature called the Moltke Foothills and close to a peninsular outcropping of valuable highland terrain. It's also close enough to the Apollo site that its tourists can ride a pressurized train to the Apollo 11 Visitors Center and survey Aldrin and Armstrong's old stomping grounds.

About That Aluminum

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The first rule for planning a base on the moon is that you want to use as much lunar material as possible. Every pound of moon rock you use is a pound of rock you don't have to ship from Earth. The lunar highlands are abundant in a mineral called anorthite, which is an amalgamation of calcium, aluminum, silicon, and oxygen.

That mixture is magic. If you can smelt the mineral into its constituent elements (and the smelting industry is a core part of Artemis), then you can the aluminum you need to build a city, the silicon you need to make glass for the city, and a happy byproduct of oxygen, which your residents need to breathe.

"The moon is made of moon bases," Weir says. "Some assembly required."

One problem with this scheme: It turns out that smelting anorthite required vast amounts of energy, far more than you could harvest via solar panels. And so there are nuclear reactors on the moon in Artemis.

Dome Sweet Dome

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Once you've got the materials, designing the outpost is pretty straightforward. Artemis, like many imagined lunar colonies, resembles a bunch of interconnected domes. "A sphere is the most efficient pressure system," Weir says. "That's the best way to hold in pressure and the strongest structural object." The city's exterior is a double-hull system, so that a puncture doesn't let out all the air and kill everyone inside. Moon rocks is stuck between the two hulls, adding strength and blocking harmful space radiation.

Artemis's domes—named for Apollo astronauts Alan Shepard, Alan Bean, Buzz Aldrin, Neil Armstrong, and Pete Conrad—aren't domes at all, actually. They're bubbles, with as much space below ground as above. It might not be romantic to live below the lunar surface, but you can't waste space.

Food, Or Something Like It

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There's no space in Artemis to grow crops for a burgeoning population. And Weir wanted to use as much real technology as possible, so you won't find any Star Trek replications. He had to devise another sustenance solution: algae.

Everyday Artemesians eat "gunk." It's a bland foodstuff made of a real kind of green algae called chlorella. What's cool about chlorella—scientifically, anyway—is that "you can fine-tune it when you grow it." It naturally contains sugars and proteins, but the balance between the two depends on the nutrients in the water and the light level the algae receives. Moon people of the future figured out how to grow huge amounts of the algae with a nutritional balance tailored to human needs.

Not that algae is a culinary delight. "I tasted it," Weir says. "It tastes awful." His fictional moon-dwellers add flavor extract to make their gunk taste like anything else.

Giant Steps

Another side effect of foregoing fake future tech is that Artemis has no artificial gravity. Tourists love playing in low gravity—"part of the fun of going to the moon is playing around in lower gravity." Residents just deal.

The real-life Apollo astronauts in their bulky spacesuits figuring out that hopping around was the best form of moon locomotion. The fictional city people of Artemis who don't need to wear all that gear found another way. They scoot about town taking long step that look a bit like everybody is ice-skating. Weir named it, simply, "The Artemis long-step." Lunar gravity simply feels natural to longtime residents. It is the tourists in the novel who can't get a handle on throwing a Frisbee on the moon.

Gravity is a heavy matter for the book's troublemaking heroine. She is in constant danger of being deported from the moon back to Saudi Arabia, a punishment that would be more than psychological. Because no human has ever grown up off-planet, nobody knows exactly what would happen to a person who grew up in low gravity and then returned to the surface of the Earth. Weir writes that Jazz would experience a long period of "gravity sickness" upon her return—which, he admits, is bit of a hand-wave. We just don't know, but it probably won't be good.

Let's Go Already

"I try to spend as little time in the real world as possible," Weir says when I ask him about the various non-fictional plans to go to the moon or Mars. I feel what he's getting at.

While Weir has written and researched book about what it'd take for people to survive on both worlds, NASA has changed course regarding its big-ticket future plans multiple times. The future of human spaceflight is tied up in arguments over where to go next: head back to the moon as a launching pad for more exploration (as with the current NASA-Russia plan for an orbiting moon station), or forego a place we've already been and get people to Mars ASAP.

If somebody is really going to be build Weir's moon city or carry the first Martians, it's probably going to be SpaceX or its ilk. "I really think the way forward is private industry," he says. Not because the approach is necessarily better than NASA's, but because NASA's priorities change every four to eight years with a new president. It's just not enough time for big, serious space mission, Weir says. "They are subject to the whims of politics."

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